Servo test bench

2. Mechanical design

The goal was to build a rigid and clean machine. Here are some examples of manufacturing methods used:

Laser cutting of the polycarbonate frame:

The panels for the box were laser cut from 10mm thick acrylic sheet. The sheet was twice as thick as the maximum cutting thickness of the machine, but the cutting was still successful except for some minor bending of the cuts. Laser cutting provides a clear and good finish to clear plastics. Some deformed cuts had to be milled afterwards. Milling leads to cloudy surfaces, as can be seen on the hole for the LDC screen. Acrylic was chosen because it lets the user also view the inner parts of the device. As a material it is quite heavy and brittle, but it seems to withstand the loads caused by the servos. 

Aluminium parts were milled:

Thin aluminium is an easy material to mill and therefore good for novice machinists. For the right parameters and overall safety, asking help from lab staff is highly recommended or even required.

Multiple custom parts were 3D-printed:

Finding the right parameters for the printer may need some iteration, as it can vary even between printers of the same model. For example, with the switch knobs it took four tries to succeed in manufacturing the right dimensions. The 3D-printers (the Ultimakers located in ADD-lab) have a short course which is required before operating the machines. By completing ENG-A1009, Practical Work Training with 3D-printers, you also gain one credit!

Holes were drilled and tapped to the frame:

Polycarbonate has a fairly low melting point, so it may get stuck into the drill flutes and cause damage to the drill bit. Also, making threads requires precision and careful use of the tools. Using screws to assemble the frame allows later disassembly and is way more rigid than hot glue or tape.